Rim and assembly of tire and/or ring-shaped tread support on same

ABSTRACT

An assembly is formed of a tire (1), a mounting rim (2), and an annular bearing support (3) for the tread (10) of the tire, for running at low pressure or at zero pressure. The rim (2) has two seats (23&#39;, 23&#34;), the first seat (23&#39;) having an outwardly inclined generatrix and being axially outwardly extended by a shoulder or hump (25&#39;), and the second seat (23&#34;) having an inwardly inclined generatrix and being axially outwardly extended by a flange (24). The tire (1) has a radial carcass reinforcement (13) with a particular meridional profile and two beads (12&#39;, 12&#34;) adapted to the mounting rim (2). The tread supporting ring (3) is ovalizable and circumferentially inextensible.

BACKGROUND OF THE INVENTION

The present invention relates to the production of mounting rims,preferably integral rims, for tires, preferably radial tires, andforming assemblies with the tires and optionally with tread supportrings, certain of which may prove useful for running in situations wherethe inflation pressure is abnormally reduced compared with the nominalpressure of use, termed the operating pressure, the inflation pressureeven being capable of becoming zero.

The main difficulties encountered when running flat or at low pressurerelate to the risk of unseating the beads of the tire, particularly therisk of unseating the bead situated on the outside of the tire mountedon the off-side of the vehicle. The techniques which have been proposed,and which are well known, for preventing unseating such as this,particularly the technique consisting of providing a shoulder or hump oflow height axially inwardly of the outer seat of the rim, tend toincrease the difficulties associated with the fitting and removal oftires.

One solution which is intended to be applied to the problem of beadsbecoming unseated is that described in French Patent 1139619, whichrelates to an assembly formed from a tire and a rim such that incontrast to the usual beads the flexible edges of the tire exert a tightgrip, under the action of the inflation pressure, on rim stops intendedto keep the said edges spaced apart from each other. This solutionrequires a carcass reinforcement which is at least special and whichdoes not comply with the compromise of properties required for apresent-day tire.

Certain previous solutions advocate the addition, to a rim as describedpreviously, of a bearing support, which is either integral or is mountedand fixed by any available means. Assemblies comprising rims with abearing support are known, both with a hump and without a hump, andGerman Application 3 626 012 and French Application 2 560 121 discloseassemblies such as these. However, they have not been generally usedbecause difficult fitting problems arise despite the progress made. Theabove-mentioned French Application describes a fitting procedure whichenables numerous difficulties to be eliminated: tilting over one of thebeads of the tire and ovalizing it enable the rim, which is providedwith its bearing support, to pass inside the tire if the rim is offeredwith its axis of rotation perpendicular to the axis of rotation of thetire casing, the beads subsequently being placed on their respective rimseats with the aid of mounting grooves situated axially on both sides ofthe bearing support.

If the overall width of the mounting rim measured axially between theends of the two flanges is termed S, D_(J) is the diameter of the rimmeasured at the level of the intersection between the rim flange and thetapered generatrix of the rim seat, the latter being viewed inmeridional section, H' is the height of the support measured withrespect to the line parallel to the axis of rotation of the rim andpassing through the point of intersection, and D_(B) is the diameter ofthe bead of the tire measured on a line parallel to the equatorial planeof the tire, which parallel line passes through the center of the beadring, the method described above is not applicable in the situationwhere the quantity 2πD_(B) is less than 2(D_(J) +2H'+S), whence it isimpossible to provide tires of the usual shape ratio with an effectiveinside support.

SUMMARY OF THE INVENTION

The present Application relates to solutions which are different fromthose disclosed in the above-mentioned Application, which similarlyenable the conditions of operation and use of a radial tire to beimproved when running at zero pressure or at low pressure whilstproviding improved protection from impacts due to pavements, thesolutions relating both to rims and to the assemblies formed by the rimsand tires adapted to such rims, with or without a removable ornon-removable tread support ring.

For this purpose, and according to the invention, a rim intended formounting a tire comprising two reinforced beads, axially delimited bytwo rim edges which are axially distant from the rim width S, andcomprising, viewed axially outwardly in meridional section with respectto the equatorial plane, a first rim seat and a second rim seat, thefirst rim seat having a generatrix, the axially outer end of which is ona circle of diameter less than the diameter of the circle on which theaxially inner end is situated is characterized in that the first rimseat is axially outwardly extended by a shoulder or hump of low heighth₁, and in that the second rim seat has a generatrix, the axially outerend of which is on a circle of diameter at least equal to the diameterof the circle on which the axially inner end is situated, the second rimseat being axially inwardly extended by a shoulder or hump of low heightand axially outwardly by a rim flange, the diameter of the flange beinggreater than the diameter of any part of the rim included between theflange and the rim edge which is axially nearest to the flange.

With regard to the properties which are sought for the assembly formedby the rim according to the invention and a tire with a structureadapted to the rim, it is advantageous if the assembly comprises a treadsupport ring. Thus, according to a variant of the invention, the rim maycomprise at least one supporting surface intended to receive a treadsupport ring, disposed axially between the axially inner ends of the tworim seats and having a generatrix, the minimum diameter of which, whichis the diameter of one of the ends of the generatrix, is at least equalto the diameter of any part of the rim axially included between the endand the rim edge corresponding to the rim seat which is axially nearestto the end. The supporting surface may be a section of revolution. Thediameter of the supporting surface is to be understood as the diameterof the parts of the supporting surface which will be in contact with thebearing support.

A mounting groove which optionally serves for the mounting of the beadson their respective rim seats has a depth and an axial width which isprimarily a function of the axial width of the beads and of the insidediameter of the reinforcement rings, bead rings for example, and ifapplicable of the width of the rim supporting surface intended toreceive the bearing support.

In certain cases the depth of the groove may appear excessive, in thatit greatly reduces the free space dedicated to mechanical runningelements. In the same manner the axial width of the mounting groove is awell known obstacle to the axial widening of the bearing support when itis advantageous to employ the latter.

With the object of minimizing the disadvantages, and according toanother variant of the invention, the rim may have two rim seats ofdifferent diameters.

In all the cases cited previously, the rim seats preferably have taperedgeneratrices forming an angle α' between 4° and 30° with the axis ofrotation, wherein the angles may be the same or different for the seats.

The rim supporting surface on to which the support ring will be slippedmay advantageously be a cylindrical supporting surface; its minimumdiameter D may advantageously be equal to the nominal diameter of therim. Similarly, it is advantageous to provide a positioning shoulder onits axially inner edge serving as an inner stop for the support ring.The mounting groove may also be disposed between this shoulder and theseat opposite to it, around which the support ring can be slipped.

The axial width L between this positioning shoulder and the axiallyouter shoulder corresponding to the seat adjacent to the section ofrevolution is advantageously equal at most to half the maximum width Sof the rim between the two rim edges. The height of the shoulder whichis axially external to the first rim seat is advantageously equal to atmost 1.25% of the nominal rim diameter of the mounting rim.

As regards the shoulder which is axially outwardly adjacent to the firstrim seat, its internal wall will preferably be tapered, the wall havinga generatrix forming a radially and axially outwardly open angle between40° and 50° with the axis of rotation of the rim.

An assembly formed by a rim and a support ring is in accordance with theinvention when the rim of the assembly is a rim having a supportingsurface and as described above, and when the tread support ring can beovalized and is preferably circumferentially inextensible and can beslipped on to the rim supporting surface.

The maximum effectiveness of the assembly according to the invention isobtained at elevated heights of the bearing support, preferably greaterthan 40% of the height of the carcass reinforcement. This characteristicprovides the advantage of prolonging the period of running flat, namelyat zero inflation pressure, without causing damage to the sidewalls ofthe tire when these are of the usual structure, or damage to the carcassreinforcement or even to the tread reinforcement.

The annular bearing support can easily be slipped on due to theparticular characteristics of the mounting rim and if its minimum insidediameter is selected to be at least equal to the minimum diameter D ofthe rim supporting surface and greater than the diameter by 2 mm atmost, its internal generatrix being parallel to the generatrix of therim supporting surface.

The bearing support, which can be ovalized and which iscircumferentially inextensible, preferably consists of vulcanized rubberin annular form, the vulcanised rubber being reinforced by wire or cordreinforcements disposed circumferentially to within 2°. A constitutionsuch as this permits ease of manipulation whilst ensuringinextensibility under all running conditions, particularly under theeffect of centrifugal forces due to high speed.

According to the invention, an assembly formed by a rim and a tire ischaracterized in that it comprises a rim as described previously and atire having a bead structure adapted to the rim.

A tire intended for the above assembly and having at least two beads ischaracterized in that the seat of the first bead has a generatrix, theaxially outer end of which is on a circle of diameter less than thediameter of the circle on which the axially inner end is situated,whilst the seat of the second bead has a generatrix, the axially outerend of which is on a circle of diameter at least equal to the diameterof the circle on which the axially inner end is situated. The tireadvantageously has a radial carcass reinforcement anchored within eachbead to a reinforcement ring. When the tire is mounted on the rim andinflated to its operating pressure, the carcass reinforcement has ameridional profile with a constant direction of curvature, at leastwithin the bead intended for mounting on the first rim seat.

The tire intended for the assembly according to the invention preferablyhas a radial carcass reinforcement, the profile of which, at leastwithin the bead intended for mounting on the first rim seat, has atangent AT at the point of tangency A with the reinforcement ring of thebead which forms an outwardly open angle φ of at least 70°, preferablygreater than 80°, with the axis of rotation.

If it is preferable that the radial carcass reinforcement of the tirehas a direction of curvature which is constant over its entire length,namely between the two points of tangency of the profile at thereinforcement rings, and the tangents of which at the points of tangencywith the reinforcement rings form outwardly open angles which arepreferably between 70° and 110° with the axis of rotation, the carcassreinforcement may advantageously have, within the bead intended formounting on the second rim seat, a meridional profile which has a pointof inflection I between a part of the profile with convex curvature anda part with concave curvature, the portion of the profile with convexcurvature having a tangent at the above point of inflection forming anaxially and radially outwardly open angle between 60° and 90° with theaxis of rotation.

In a tire which is advantageous for carrying out the invention, the beadseats are tapered and each seat forms an angle between 10° and 45° withthe axis of rotation, an angle which is inwardly axially open andoutwardly radially open for the bead seat intended for mounting on thefirst rim seat, and an angle which is axially and radially outwardlyopen for the bead seat intended for mounting on the second rim seat.

The tip of the bead which is intended for mounting on the first rim seatmay be truncated; in other words, the bead seat or base will be joinedto the tip side of the bead by a straight segment inclined in relationto a line parallel to the axis of rotation at an angle which is radiallyand axially outwardly open and which is less than 90°, preferably equalto 45°±5°, the tip of the bead being the part of the bead correspondingto the end of the bead seat which is nearest to the axis of rotation,whilst the heel of the bead is the part of the bead corresponding to themost distant end of the bead seat. The bead heels of the tire accordingto the invention are also advantageously truncated, the bead seats thenbeing extended axially on the heel side by generatrices forming anglesbetween 40° and 50° with the axis of rotation.

The beads are mounted on the rim, and in particular on the truncated rimseats, with a certain grip. For the assembly considered, this grip isdefined as the ratio of the minimum diameter of the rim seat to theminimum diameter of the bead seat. The grip will preferably be at leastequal to 1.003, whilst remaining less than 1.02.

Apart from the fact that the assembly according to the invention solvesthe problem of beads becoming unseated whilst minimising the problems offitting tires in all the situations which usually arise, the particularstructure of the tire, and more particularly of the beads of the tire,provide other advantages.

In practice, if ovalization of the beads of a tire is a necessaryoperation for the fitting of the said tire, and even though theconstitution of certain bead reinforcement rings, particularly beadrings of the "plaited" type, enable ovalization to be effected easily,this manipulation must not exceed certain limits. In particular,ovalization which is too pronounced, which is the case in the prior artdescribed above, seriously affects the rigidity of a bead ring, namelyunder a tensile force, under a bending force on edge, or under a bendingforce in its plane, which under some conditions of running of the tiremanifests itself as an impairment of the properties of the resistance tounseating, of the fatigue strength of the beads and of the resistance toblow-outs. These properties are maintained by the invention.

DESCRIPTION OF THE DRAWING

The invention will be better understood with reference to the drawingsattached to the description, which illustrate non-limiting examples of a185/33-16 tire mounted on a rim of diameter equal to 406.4 mm, andwhere:

FIG. 1 is a meridional section through a rim according to the invention;and

FIG. 2 is a meridional section through an assembly comprising a rim, atire with an adapted structure and a tread support ring.

DESCRIPTION OF PREFERRED EMBODIMENTS

The rim 2, which has a width S measured between its ends which areaxially the most distant from the equatorial plane XX', is formed goingfrom one end to the other from a shoulder or hump 25', the inside faceor wall of which forms an angle γ', which is equal to the angle γ of theexternal face 12A of the tip of the bead 12' of the tire 1, with theaxis of rotation of the rim, and the diameter of which D_(S), which isequal to 402 mm, is less than the inside diameter D_(T) of thereinforcement ring 14, which in the example described is a bead ring ofthe "plaited" type (FIG. 3). The height h₁, which is measured withrespect to the axially outer end of the rim seat 23', is equal to atmost 1.25% of the nominal rim diameter D, the nominal rim diameter Dbeing the diameter of the ends of the rim seats which are radially themost distant from the axis of rotation, as is generally accepted in thesituation described comprising a rim where the two seats have the samediameter. This nominal diameter is equal to 406.4 mm.

The shoulder 25' is axially inwardly extended by the rim seat 23' whichitself is axially adjacent to a section of revolution 21. The section ofrevolution has a cylindrical generatrix of diameter D, and thiscylindrical section is provided axially inwardly with a positioning stop26, this stop serving, as its name indicates, to position the treadsupport ring which is to be slipped on to the section of revolution. Theheight h₂ of this stop is equal at most to 1.5% of the nominal diameterD of the rim 2, and in the example described is equal to 5 mm. The axialdistance L, measured between the end of the shoulder 25' and the insideface of the stop 26, is equal to 103 mm. This value is less than halfthe width of the rim 2, which is equal to 215 mm.

The mounting groove 22, which axially extends the section of revolutionprovided with its positioning stop, has a depth h' of 50 mm, this heighth' being measured radially from the axial line defining the nominaldiameter D of the rim. The seat 23", which is firstly provided axiallyinwardly with a shoulder or hump 25" of height equal to 3 mm in thesituation described, and which is secondly axially outwardly adjacent toa rim flange 24, completes the rim 2. The seat 23" has a generatrix, theaxially inner end of which is on a circle of diameter less than thediameter of the circle on which the axially outer end of the seat 23" issituated, the axially outer end being situated on a circle of diameterD, which is also the nominal diameter and the diameter of the seat 23'.As regards the rim flange 24, this has the known shape of the rimflanges which are usual and which have been standardized byinternational authorities, namely it is composed of a first part 24'perpendicular to the axis of rotation of the rim, the first part beingextended axially and radially outwardly by a second curved part 24". Theflange 24 has a diameter D_(F) of 432 mm, which is greater than thediameter D of the section of revolution.

The two rim seats 23' and 23" have tapered generatrices, which form anangle α' between 4° and 30° with the axis of the rotation of the rim. Inthe example described this angle is equal to 14°.

In FIG. 2, the assembly E comprises the rim 2 as shown in FIG. 1, a tire1 having an adapted bead structure, and a tread support ring 3. The tire1 comprises a tread 10 joined by means of two sidewalls to two beads 12'and 12". It is reinforced by a radial carcass reinforcement 13 formedfrom a single ply of textile cords anchored within each bead 12', 12" byupturn around a bead ring 14, which in the example illustrated is of the"plaited" type. The carcass reinforcement is topped by a treadreinforcement 15. The tire 1 preferably has a shape ratio equal at mostto 0.7, and more particularly less than 0.5. The term "shape ratio" isto be understood as the H/B ratio of the carcass reinforcement, H beingthe height of the carcass reinforcement 13 and B its maximum axialwidth. The height H is the radial distance separating the point T of thecarcass reinforcement, which is the most distant from the axis ofrotation, from the axial line passing through the center of gravity O ofthe section of bead ring 14 which is nearest to the axis of rotation. Inthe situation described H is equal to 63 mm, the tire considered havinga shape ratio equal to 0.33. The maximum axial width B is equal to 190mm.

On the side of the assembly corresponding to the first rim seat 23', andwithin the bead 12', the carcass reinforcement 13 has a meridionalprofile, the tangent AT of which at point A on the bead ring forms anoutwardly open angle φ of 85°. On the side of the assembly correspondingto the second rim seat 23", and within the bead 12", the carcassreinforcement has a meridional profile which has a point of inflectionI. Radially above this point of inflection, the reinforcement profile isconvex; radially below this point of inflection, the reinforcementprofile is concave and forms a tangent to the bead ring 14 at point A,whereas at point I, the tangent IT' to the meridional profile forms anangle φ' equal to 75° with the axis of rotation of the tire.

Each bead 12', 12", which has an axial width comparable with the known,usual bead widths, has a bead seat with a tapered base 12B which formsan angle α between 10° and 45° with the axis of rotation. In thesituation described this angle is equal to 22° and greater than theangle α', which is the angle of the rim seats. On the side of theassembly corresponding to the first rim seat 23' the bead seat 12B isaxially outwardly extended by the outer face 12A of the bead tip, and isaxially inwardly extended by a tapered generatrix 12C corresponding tothe heel of the bead 12'. On the side of the assembly corresponding tothe second rim seat 23" the bead seat 12B is axially outwardly extendedby a tapered heel generatrix 12C, whilst the said seat 12B is inwardlyaxially joined to the inside wall of the tire in the usual manner.

As regards the tread support ring (3), its meridional section has ashape which approximates to that of a rectangle, the radially inner sideof which is rectilinear, whilst the lateral sides and the radially outerside may be slightly curved. The difference H' between its internalradius and its external radius is equal to 31 mm, which represents 50%of the height H of the tire (1).

It consists of vulcanized rubber, reinforced radially internally andradially externally, respectively, by a reinforcement (31) consisting oftwo plies of textile cords oriented at approximately 2°. Since in thesituation described the diameter of this support ring is equal to thediameter D' of the section of revolution 21, it can easily be slipped onto the section of revolution.

We claim:
 1. A rim (2) intended for mounting a tire (1) comprising tworeinforced beads (12', 12"), axially delimited by two rim edges whichare axially separated by the rim width S, and comprising, viewed axiallyoutwardly in meridional section with respect to the equatorial plane, afirst rim seat (23') and a second rim seat (23"), the first rim seat(23') having a generatrix, the axially outer end of which is on a circleof diameter less than the diameter of the circle on which the axiallyinner end is situated, the rim characterized in that the first rim seat(23') is axially outwardly extended by a shoulder or hump of low heighth₁ and in that the second rim seat (23") has a generatrix, the axiallyouter end of which is on a circle having a diameter at least equal tothe diameter of the circle on which the axially inner end is situated,the said second rim seat (23") being axially inwardly extended by ashoulder or hump (25") of low height, and axially outwardly by a rimflange (24), the diameter of the said flange being greater than thediameter of any part of the rim included between the said flange and therim edge which is axially nearest to the said flange.
 2. A rim accordingto claim 1, characterized in that it comprises at least one supportingsurface (21) intended to receive a tread support ring (3), disposedaxially between the axially inner ends of the two rim seats (23', 23")and having a generatrix, the minimum diameter of which is at least equalto the diameter of any part of the rim axially included between the saidend and the rim edge corresponding to the rim seat which is axiallynearest to the said end.
 3. A rim according to claim 2, characterized inthat the at least one supporting surface (21) includes a supportingsurface axially adjacent to the first rim seat (23').
 4. A rim accordingto claim 2, characterized in that the at least one supporting surface(21) is one supporting surface onto which the support ring (3) will beslipped and has a cylindrical generatrix, the minimum diameter D ofwhich is equal to the nominal diameter of the rim, the said supportingsurface optionally being provided on its axially inner edge with apositioning shoulder (26) serving as an inner stop for the support ring(3).
 5. A rim according to claim 1, characterized in that it comprisesat least one mounting groove (22), which at least one groove extendsaxially inwardly of the second rim seat (23") and its shoulder or hump(25").
 6. A rim according to claim 1, characterized in that the rimseats (23', 23") have tapered generatrices forming an angle α' between4° and 30° with the axis of rotation.
 7. A rim according to claim 1,characterized in that the rim seats (23', 23") have tapered generatricesforming angles α' with the axis of rotation which are different fromeach other.
 8. An assembly of a rim (2) and a tread support ring (3),the rim (2) of the assembly comprising, viewed axially outwardly inmeridional section with respect to the equatorial plane, a first rimseat (23') and a second rim seat (23"), the first rim seat (23') havinga generatrix, the axially outer end of which is on a circle of diameterless than the diameter of the circle on which the axially inner end issituated, the rim characterized in that the first rim seat (23') isaxially outwardly extended by a shoulder or hump of low height h₁ and inthat the second rim seat (23") has a generatrix, the axially outer endof which is on a circle having a diameter at least equal to the diameterof the circle on which the axially inner end is situated, the saidsecond rim seat (23") being axially inwardly extended by a shoulder orhump (25") of low height, and axially outwardly by a rim flange (24),the diameter of the said rim flange being greater than the diameter ofany part of the rim included between the said flange and the rim edgewhich is axially nearest to the said flange, a supporting surface (21)for receiving the tread support ring (3), the supporting surface beingdisposed axially between the axially inner ends of the two rim seats(23', 23") and having a generatrix, the minimum diameter of which is atleast equal to the diameter of any part of the rim axially includedbetween the said end and the rim edge corresponding to the rim seatwhich is axially nearest to said end, the tread support ring (3) beingreceived on said supporting surface (21), the tread support ring (3)being characterized in that it is circumferentially inextensible and canbe ovalized and slipped onto the supporting surface.
 9. An assembly of arim (2) and a tire (1), the rim comprising, viewed axially outwardly inmeridional section with respect to the equatorial plane, a first rimseat (23') and a second rim seat (23"), the first rim seat (23') havinga generatrix, the axially outer end of which is on a circle of diameterless than the diameter of the circle on which the axially inner end issituated, the rim characterized in that the first rim seat (23') isaxially outwardly extended by a shoulder or hump of low height h₁ and inthat the second rim seat (23") has a generatrix, the axially outer endof which is on a circle having a diameter at least equal to the diameterof the circle on which the axially inner end is situated, the saidsecond rim seat (23") being axially inwardly extended by a shoulder orhump (25") of low height, and axially outwardly by a rim flange (24),the diameter of the said rim flange being greater than the diameter ofany part of the rim included between the said flange and the rim edgewhich is axially nearest to the said flange, said tire having tworeinforced beads (12', 12"), the seat of the first bead (12') having ageneratrix, the axially outer end of which is on a circle of diameterless than the diameter of the circle on which the axially inner end issituated, while the seat of the second bead (12") has a generatrix, theaxially outer end of which is on a circle of diameter at least equal tothe diameter of the circle on which the axially inner end is situated,and a radial carcass reinforcement (13) anchored within each bead (12',12") to a reinforcement ring (14), the said carcass reinforcementhaving, when the tire is inflated to its operating pressure, ameridional profile with a constant direction of curvature at leastwithin the first bead (12'), the tangent AT of which at the point oftangency A with the reinforcement ring (14) of the first bead (12')forms an outwardly open angle φ of at least 70° with the axis ofrotation.
 10. An assembly according to claim 9, characterized in thatwhen the tire is inflated to its operating pressure the said carcassreinforcement (13) has a meridional profile, the direction of curvatureof which is constant over its entire length, and the tangents AT at thepoints of tangency A of the said profile with the reinforcement rings(14) of the beads (12', 12") form outwardly open angles φ between 70°and 110° with the axis of rotation.
 11. An assembly according to claim9, characterized in that when the tire is inflated to its operatingpressure the said carcass reinforcement (13) has a meridional profilewhich has a constant direction of curvature within the first bead (12')and the tangent AT of which at the point of tangency A with thereinforcement ring (14) of the first bead (12') forms an outwardly openangle φ of at least 70° with the axis of rotation, and which has a pointof inflection I in the second bead (12") which is a transition pointfrom a convex curvature of the said profile to a concave curvature ofthe said profile, the said portion of the profile with convex curvaturehaving a tangent IT' at the point of inflection I forming an axially andradially outwardly open angle φ' between 60° and 90° with the axis ofrotation.
 12. An assembly of a rim (2), a tread support ring (3), and atire (1), the rim comprising, viewed axially outwardly in meridionalsection with respect to the equatorial plane, a first rim seat (23') anda second rim seat (23"), the first rim seat (23') having a generatrix,the axially outer end of which is on a circle of diameter less than thediameter of the circle on which the axially inner end is situated, therim characterized in that the first rim seat (23') is axially outwardlyextended by a shoulder or hump of low height h₁ and in that the secondrim seat (23") has a generatrix, the axially outer end of which is on acircle having a diameter at least equal to the diameter of the circle onwhich the axially inner end is situated, the said second rim seat (23")being axially inwardly extended by a shoulder or hump (25") of lowheight, and axially outwardly by a rim flange (24), the diameter of thesaid rim flange being greater than the diameter of any part of the rimincluded between the said flange and the rim edge which is axiallynearest to the said flange, a supporting surface (21) for receiving thetread support ring (3), the supporting surface being disposed axiallybetween the axially inner ends of the two rim seats (23', 23") andhaving a generatrix, the minimum diameter of which is at least equal tothe diameter of any part of the rim axially included between the saidend and the rim edge corresponding to the rim seat which is axiallynearest to said end, the tread support ring (3) being received on saidsupporting surface (21), the tread support ring (3) being characterizedin that it is circumferentially inextensible and can be ovalized andslipped onto the supporting surface, said tire having two reinforcedbeads (12', 12"), the seat of the first bead (12') having a generatrix,the axially outer end of which is on a circle of diameter less than thediameter of the circle on which the axially inner end is situated, whilethe seat of the second bead (12") has a generatrix, the axially outerend of which is on a circle of diameter at least equal to the diameterof the circle on which the axially inner end is situated, and a radialcarcass reinforcement (13) anchored within each bead (12', 12") to areinforcement ring (14), the said carcass reinforcement having, when thetire is inflated to its operating pressure, a meridional profile with aconstant direction of curvature within the first bead (12'), the tangentAT of which at the point of tangency A with the reinforcement ring (14)of the first bead (12') forms an outwardly open angle φ of at least 70°with the axis of rotation, and with a point of inflection I in thesecond bead (12") which is a transition point from a convex curvature ofthe said profile to a concave curvature of the said profile, the saidportion of the profile with convex curvature having a tangent IT' at thepoint of inflection I forming an axially and radially outwardly openangle φ' between 60° and 90° with the axis of rotation.
 13. An assemblyaccording to claim 12, the rim including a mounting groove (22) whichextends axially inwardly of the second rim seat (23") and its shoulderor hump (25").